Glutamine-dependent NAD+ synthetase. How a two-domain, three-substrate enzyme avoids waste.

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Wojcik M, Seidle HF, Bieganowski P, Brenner C

Glutamine-dependent NAD+ synthetase. How a two-domain, three-substrate enzyme avoids waste.

J Biol Chem. 2006 Nov 3;281(44):33395-402. Epub 2006 Sep 5.

PubMed ID

16954203 [ View in PubMed

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Abstract

Glutamine-dependent NAD(+) synthetase, Qns1, utilizes a glutamine aminotransferase domain to supply ammonia for amidation of nicotinic acid adenine dinucleotide (NaAD(+)) to NAD(+). Earlier characterization of Qns1 suggested that glutamine consumption exceeds NAD(+) production by 40%. To explore whether Qns1 is systematically wasteful or whether additional features account for this behavior, we performed a careful kinetic and molecular genetic analysis. In fact, Qns1 possesses remarkable properties to reduce waste. The glutaminase active site is stimulated by NaAD(+) more than 50-fold such that glutamine is not appreciably consumed in the absence of NaAD(+). Glutamine consumption exceeds NAD(+) production over the whole range of glutamine and NaAD(+) substrate concentrations with greatest efficiency occurring at saturation of both substrates. Kinetic data coupled with site-directed mutagenesis of amino acids in the predicted ammonia channel indicate that NaAD(+) stimulates the glutaminase active site in the k(cat) term by a synergistic mechanism that does not require ammonia utilization by the NaAD(+) substrate. Six distinct classes of Qns1 mutants that fall within the glutaminase domain and the synthetase domain selectively inhibit components of the coordinated reaction.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
L-Glutamine	Glutamine-dependent NAD(+) synthetase	Protein	Humans	Unknown	Substrate	Details